Quarkonium production in hadronic collisions is a complex mechanism involving hard-scale processes, i.e., the creation of the quark–antiquark pair in the initial hard scattering, as well as the subsequent soft-scale process of the binding of the pair into a colorless final state [1]}.
The production mechanism is sensitive to the gluon content of the colliding hadrons and thus to the parton distributions of the incoming proton (PDF) or nucleus (nPDF) [2]}, [3]}.
In collisions involving heavy nuclei, modification to the production with respect to that in pp collisions may also arise from, e.g., energy loss that the heavy quarks experience while traversing the nucleus [4]} or from subsequent interactions of the final states with comoving matter [5]}, both of which lead to a suppression of the quarkonium yield.
Good understanding of these phenomena is imperative in order to correctly interpret the data from nucleus–nucleus collisions, where quarkonia are expected to be suppressed due to a deconfined partonic medium, i.e., the quark–gluon plasma (QGP) [6]}. At the energies reached by the Large Hadron Collider (LHC), the suppression is partially compensated by a regeneration of the bound states in the medium [7]}.
